The commercial production of ammonium perchlorate is carried out in a process which reacts anhydrous ammonia, concentrated aqueous hydrochloric acid and concentrated sodium perchlorate solutions. Because of its strong oxidizing power and chemical stability, ammonium perchlorate (AP) provides a reliable means of high-energy oxidation under controlled conditions. It is especially useful when employed in a composite propellent with plastic fuel binders. In this application, it currently dominates the field as the oxidizer of choice in high performance, solid propellants.
The pH of the reaction mixture is maintained close to neutral as it is fed into a crystallizer. The reaction mixture, maintained at a temperature of about 35.degree. C., is passed through a vaporizer which produces a super-saturated solution. The super-saturated solution is fed through a bed of ammonium perchlorate crystals where the excess crystallizers. The ammonium perchlorate slurry formed is fed to a centrifuge where the mother liquor is removed and recycled to the crystallizer. The AP crystals are washed and dumped into a saturated solution of ammonium perchlorate which removes the last traces of chloride. Ammonium perchlorate crystals are then separated and dried. When used as a solid propellant, the key requirements for ammonium perchlorate are burn rate, product purity and stability. Impurities present impact crystal growth, product stability and overall process economics. Product purity is so important that current commercial processes, due to the extensive purification steps involved, operate at low efficiences in order to produce a highly pure product. However, ammonium perchlorate produced by current technology contains 15-400 parts per million of sodium as well as many other metallic and non-metallic impurities in the finished product.
U.S. Pat. No. 3,307,903 published Mar. 7, 1967 by F. Lazari teaches a process for preparing ammonium perchlorate in a solution crystallization process in which gaseous ammonia is introduced to neutralize a perchloric acid solution to form a saturated solution of NH.sub.4 ClO.sub.4 which is fed to a crystallization vessel. The perchloric acid is prepared by the reaction of sodium perchlorate with sulfuric acid with the reaction mixture being distilled under vacuum to recover a solution of perchloric acid.